I have five nine week old Isa browns. Very active and curious and enjoy new foods. They are currently in a shed as their coop is not built yet. However, whenever they come across dirt, particularly dry sand (plenty of that in Perth) they will eat it. Are they lacking something in their diet? I believe they need some small stones/gravel if they are eating larger grains but most of their diet is small grower pellets and green vegetables. Do I need to worry or do they know what is good for them?